Materials using rare-earth elements are being used in various fields such as for medical supplies (X-ray films), permanent magnets, glass abrasives, glass coloring substances, ultrasmall lenses, phosphors, magnetic disks, lasers and the like, and are known as industrially important metal elements. Although materials containing rare-earth elements were conventionally used as bulk materials, pursuant to the development of advanced information society in recent years, these materials are now being used as thin films or layered films containing dissimilar materials for fabricating a new devices. For example, pursuant to the highly information-oriented society centering on the Internet, demands are increasing for flat panel displays (hereinafter referred to as “FPD”) as represented by liquid crystal displays (hereinafter referred to as “LCD”), plasma displays (hereinafter referred to as “PDP”), field emission displays (hereinafter referred to as “FED”), and organic EL displays. Among them, the use of rare-earth oxide as the phosphor film of full-color FED and vacuum fluorescent display (VFD) is being considered. Further, in order to miniaturize and reduce the power consumption of semiconductor integrated circuits and semiconductor devices used in computers and mobile phones in which further technical advantages are expected, the necessity for making a gate insulation film a high dielectric constant insulation film (High-K insulation film) is increasing, and the use of rare-earth oxide films formed of Y2O3, La2O3, CeO2, Sm2O3, Eu2O3, Gd2O3, Tb2O3, Dy2O3, Ho2O3, Er2O3, Tm2O3, Yb2O3, Lu2O3 and the like as the gate insulation film is being considered. In addition, in order to create a high performance device using a metal oxide thin film, the manufacture of an epitaxial metal oxide thin film obtained by controlling the crystal orientation of the thin film is becoming essential, and rare-earth oxide is being used as an buffer layer for preparing epitaxial thin films from the perspective of crystal structure and chemical stability. For instance, when fabricating metal oxide such as a ferroelectric material or an infrared sensor material on a silicon substrate, a rare-earth oxide thin film formed from cerium oxide or the like can be used as the buffer layer in order to alleviate the lattice mismatch of the silicon substrate and the ferroelectric material and control the generation of an impurity phase. Like this, since the application of rare-earth metal oxide thin films is wide-ranging, these thin films are crucially important materials for the sustained development of a highly information-oriented society. Nevertheless, in all of the foregoing cases, since high-temperature heat treatment is required to prepare the thin films, reaction at the substrate and rare-earth oxide film interface and deterioration of the substrate caused major problems. The present invention relates to the manufacturing method and usage of a crystallized metal oxide thin film for use as a DRAM capacitor, a plasma-resistant thin film, a phosphor film, an epitaxial thin film, an infrared sensor device buffer layer, superconducting device buffer layer and a dielectric device buffer layer.
FED is a display device based on the fundamental principle of emitting electrons from a planate emitter into a vacuum, and colliding such electrons with phosphor to emit light. In this technology, a device corresponding to an electron gun of a cathode ray tube is formed in a planar shape, and a bright and high-contrast screen like a cathode ray tube (hereinafter referred to as “CRT”) is realized in a large flat-panel display. With CRT, one electron gun that emits electrons is positioned a dozen to several ten centimeters away from the light-emitting surface. Meanwhile, with FED, electrodes in the form of minute protrusions are arranged on a glass substrate in a lattice pattern in an equal number as the number of pixels, and the respective electrodes discharge electrons toward the phosphors that are arranged to face each other in several millimeter intervals on the glass substrate. Since the deflection required in CRT is no longer necessary, it is possible to fabricate a large flat-screen display, and the power consumption can also be reduced to roughly half of a CRT display. FED is considered to be promising technology that will realize large flat-screen televisions/displays for the next generation along with LCD and PDP.
With conventional manufacturing methods of a phosphor film, after the preparation of particulates, screen printing was used to manufacture the phosphor film. In order to put full-color FED into practical use, various phosphors that are highly efficient and have minimal effect on the field emitter are essential, and this is the high-priority issue in realizing full-color FED. Heretofore, materials with high probability of being used as the FED phosphor were as follows. Red: [SrTiO3:Pr, Y2O3:Eu], blue: [Zn(Ga, Al)2O4:Mn, Y3(Al, Ga)5O12, ZnS:Cu, Al], blue: [Y2SiO5:Ce, ZnGa2O4, ZnS:Ag, Cl] and so on. While nonoxide phosphor is unstable to electron beams, oxide phosphor is stable and attracting attention as the FED phosphor.
Nevertheless, since conventional phosphor films were fabricated with a binder, there is a problem in that it is not possible to maintain high luminous efficiency due to the discharge of gas by electron beam irradiation. As one method of overcoming this problem, the possibility of improving characteristics by directly manufacturing a rare-earth phosphor film on a glass substrate is being considered.
As representative manufacturing methods of Y2O3 thin films, the following have been reported: electron beam evaporation (Applied Surface Science, 212-213 (2003) 815; “Non-Patent Document 1”), sputtering method (Japanese Patent Laid-Open Publication No. 2005-68352; “Patent Document 1”), sol-gel method (Japanese Patent Laid-Open Publication No. 2002-235078; “Patent Document 2”), and atomization thermal decomposition method (Journal of Luminescence, 93 (2001) 313; “Non-Patent Document 2”).
Nevertheless, since all of the foregoing methods include the step of subjecting the substrate to heat treatment at a high temperature of 500° C. to 1000° C., it was difficult to form a thin film on an organic substrate or a glass substrates or a Si substrate.
Further, since a rare-earth oxide such as Y2O3 has a large dielectric constant, it can be used as a DRAM capacitor (Japanese Patent Laid-Open Publication No. 2005-150416; “Patent Document 3”). Normally, since silicon is used as the lower electrode, it is desirable to prepare the thin film at a low temperature that will not cause an oxidation reaction.
Similarly, it is also possible to use a rare-earth oxide film formed from Y2O3 or the like as a buffer layer on silicon or a single crystal substrate (Japanese Patent Laid-Open Publication No. 1997-162088; “Patent Document 4”). Patent Document 4 uses a CeO2 (cerium oxide) tablet to prepare a CeO2 epitaxial layer on a silicon substrate with the electron beam evaporation method at 800° C. Nevertheless, when there is a read circuit containing an organic material or an aluminum wiring, it is difficult to prepare the device since such read circuit will be broken. As described above, the application of rare-earth thin films is wide-ranging, and, since such thin film is a crucially important industrial material, preparation of new devices will be enabled by developing crystal growth technology at a low temperature of 500° C. or lower,
As a method of preparing a certain type of metal oxide film, a manufacturing method of a metal oxide and a metal oxide thin film based on an excimer laser, comprising the steps of dissolving metal organic acid salt or an organic metal compound MmRn (provided M=4b group elements of Si, Ge, Sn, Pb; 6a group elements of Cr, Mo, W; 7a group elements of Mn, Tc, Re; R=an alkyl group such as CH3, C2H5, C3H7, C4H9; or a carboxyl group such as CH3COO−, C2H5COO−, C3H7COO−, C4H9COO−; or a carbonyl group of CO; wherein m and n are integers) in a soluble solvent (or if a liquid, using it as is), dispersively applying such solution on a substrate, and subjecting the resultant substrate to irradiation with an excimer laser under an oxygen environment, is known. (Specification of Japanese Patent No. 2759125; “Patent Document 5”).
In addition, there is a method of manufacturing a metal oxide on a substrate without heat treatment at a high temperature as performed in a conventional metalorganic deposition. For instance, a manufacturing method of a metal oxide for forming a metal oxide on a substrate, comprising the steps of dissolving a metal organic compound (metal organic acid salt, metal acetylacetonato, metal alkoxide including an organic group of carbon number 6 or greater) in a solvent to obtain a solution, applying such solution on a substrate, thereafter drying the substrate, and subjecting the resultant substrate to irradiation with a laser beam having a wavelength of 400 nm or less, is known. (Japanese Patent Laid-Open Publication No. 2001-31417; “Patent Document 6”).
Patent Document 6 describes a manufacturing method of a metal oxide for forming a metal oxide on a substrate, comprising the steps of dissolving a metal organic compound in a solvent to obtain a solution, applying such solution on a substrate, thereafter drying the substrate, and subjecting the resultant substrate to irradiation with a laser beam having a wavelength of 400 nm or less; for instance, an excimer laser selected from ArF, KrF, XeCl, XeF and F2, and further describes that the irradiation of the laser beam having a wavelength of 400 nm or less is performed in a plurality of stages, wherein the initial stage of irradiation is performed with weak irradiation that will not completely decompose the metal organic compound, and the subsequent stage of irradiation is performed with strong irradiation that will even change the oxide. Further, it is also known that the metal organic compound is a compound comprising two or more types of different metals, the obtained metal oxide is a compound metal oxide comprising different metals, and the metal of the metal organic acid salt is selected from a group comprised of iron, indium, tin, zirconium, cobalt, iron, nickel and lead.
Furthermore, a manufacturing method of a compound oxide film comprising the steps of applying and depositing a precursor coating solution containing a starting material component of the respective oxides of La, Mn and Ca, Sr or Ba on the substrate, thereafter the crystallized thin film was formed on the substrate, and forming a compound oxide film (that does not show superconductivity) having a perovskite structure as represented with the composition formula of (La1−xMx)MnO3−δ(M:Ca, Sr, Ba, 0.09≦x≦0.50), wherein after applying and depositing the precursor coating solution on the substrate, the thin film is crystallized by laser irradiation light having a wavelength of 360 nm or less on the thin film formed on the substrate.(Japanese Patent Laid-Open Publication No. 2000-256862; “Patent Document 7”).
Here, as the irradiating light source, ArF excimer laser, KrF excimer laser, XeCl excimer laser, XeF excimer laser, third harmonic generation of YAG laser, or fourth harmonic generation of YAG laser is used for the preparation of the oxide thin film, and the precursor coating solution to be applied on the substrate is obtained by mixing, reacting and adjusting an alkanolamine coordinate compound of La, carboxylate of Mn, and metal or alkoxide of M in a primary alcohol in which the carbon number is 1 to 4.